Nowadays, in public places such as banks and shopping malls, monitoring devices, e.g., probes, cameras, etc., can usually be seen at ceilings or corners, and are used for supervising people's behavior. In general, common monitoring devices collect image signals, and people can know the process, cause, and specific situation of an event that has occurred from image data recorded by a monitoring device. For example, traffic police can reproduce the course of a traffic accident that has occurred according to images recorded by a road monitoring probe, policemen can track down a suspect's escape route by means of a bank or road monitoring probe, etc. These monitoring devices play an important role in monitoring and reproducing an event that has occurred in people's living environment, so to speak.
However, at least the following problems exist in the prior art: in practical applications, a monitoring device needs to store a large amount of video data every day, and most of the video data may be useless and thus wastes the storage space of a hard disk of the monitoring device to a great extent, and in the meanwhile, when an event occurs, related personnel cannot extract key video data quickly.